There's no great shock that Arizona will not be chasing after the very top free-agent starters: there isn't enough money in the budget. Scherzer already declined a six-year, $144 million contract offer from the Tigers prior to the 2014 season, and going 18-5 with a 3.15 ERA will hardly have dropped his price. Estimates of what he'll get include seven years at an average of $26 million per season, likely too rich for the Diamondbacks, even allowing for the new television contract that will kick in after next year, which could help fund such an offer. But even if the money was there, Scherzer will be 37 at the end of a seven-year deal, likely well into the downside of his career.
Kenta Maeda would be a younger, cheaper alternative, currently being aged only 26. However, at this point, it's not even clear if his club, the Hiroshima Carp, will make him available through the posting system this winter. Indeed, last month, team owner told The Japan Times, "the team is unlikely to accept tender bids for Kenta Maeda under the posting system this offseason following the right-hander’s disappointing season in 2014." He's under their control through the end of the 2016 season, and naturally, they want to maximize the return on their investment, in terms of the resulting posting fee, by offering him when his value is highest.
We should also perhaps clarify what we mean by "disappointing," since Maeda's ERA this season was 2.60, with 161 strikeouts in 187 innings of work. That certainly doesn't sound bad, but it was an ERA half a run higher than 2013, and a full run worse than 2012, when it was 1.53. However, in Maeda's defense, he was apparently adopting the Bronson Arroyo approach to pitching, working through a litany of niggling injuries this season that included elbow tightness, a bruised thigh, and tightness/inflammation in his left side, but only caused him to skip a start once.
All told, over his seven seasons in Japanese baseball, here are how his stats compare against the previous couple of Japanese free-agent pitcher, Masahiro Tanaka - whom, of course, the Diamondbacks pursued but failed to sign last winter - and Yu Darvish [you should bear in mind Japan changed the baseballs used in 2013, after Darvish left, leading to a 40% increase in HR rate that year]
The raw numbers are not dissimilar to Tanka: a few less hits, but also a lower strikeout rate, and a significantly higher home-run rate - though I've no idea whether park factors have an effect on the latter number. Generally, the opinion seems to be that Maeda is definitely inferior, with some reports critical in particular of his slider, with too many hanging offerings, which you might get away with in Japan, but would likely be an issue in the major leagues. He's also very lightly built, listed at only 154 lbs. For comparison, the median MLB pitcher last year, per B-R.com, was 210 lbs, with only one starter (the A's Jesse Chavez) less than 170.
Nick Piecoro spoke to some scouts about Maeda, one of whom addressed this. "Maeda isn't as physical as Tanaka or Darvish. That's a concern that he's a bit of a smaller guy, like a Roy Oswalt body type. But he has tremendous feel for pitching and can throw five different pitches. I've seen him up to 95 before, so he has that, but he has other things he can try to go to that he can get you out with." The general opinion was "mid-rotation type" or "solid No. 4 starter," though one did recall how Tanaka was under-rated: "I think a lot of scouts saw him as a No. 2 or 3 type, but you saw what he did. You can never really tell."
Writing before the 2014 campaign, Patrick Newman of NPB Tracker compared Maeda to Kenshin Kawakami, though added "Maeda is younger, healthier and more consistent than Kawakami was." Kawakami spent two seasons in the majors with the Atlanta Braves, giving them an ERA+ of 94, though with an ugly W-L record of 8-22. It's worth noting that he didn't make his big-league debut until a couple of months before his 34th birthday. But he may be a good comparison for Maeda, in terms of being a player who was able to achieve some success by pitching i.e. location and keeping hitters off-balance, rather than overwhelming them with pure "stuff".
The change in rules for posting players, capping the negotiating fee at a maximum of $20 million, should certainly level the playing field in terms of entry to the dance [if that's not mixing my metaphors horribly!]. Just as they were with Tanaka, the D-backs certainly have the chance to be in the conversation with Maeda. But they are unlikely to be the only ones. As we saw last year, it's then closing the deal, when competing against teams who may well have check-books open wider than Arizona, that will prove the tougher part of the exercise.
Here's a video of Maeda pitching in last year's World Baseball Classic, so you can get some idea of the type of pitcher he is.